What size SWA cable to garden room?

This is by no means a diy job. That 6mm you have been given is too small for a start given distance, load expectancy, and method of installation. Best bet contact a registered electrician who would do a load calculation for cable size, also your method of earthing. But as it’s not a diy job as it needs designing, installing and testing and a certificate issued. Good luck.

You need to find out your worst case scenario for the maximum kw used, maximum temperature (I know it’s outside but we’ve had summers in excess of 40’C (I’ve calculated a job for someone for a kilm at 7kw plus 1kw lighting and the cable will be 10mm over 50mts) so without taking everything into account, it would be difficult to answer this question.

I think it would be right to get an electrician over to discuss what you need and then carry out a site survey to check the requirements of the installation. Most trades are professional and do numerous jobs like this and may actually save you money and give you good advice to get what you want right. For a start there are a number of variables that can have a big impact on an installation like this. Failing to calculate things such as design current (which will be affected by your choice of appliances and there associated power rating) current carrying capacity of the cable (taking in to account installation method), voltage drop (which will be affected by the length and diameter of cable) and relevant information in respect of protective devices can have the consequence of the installation not being fit for service and potentially dangerous. All the work would then require full testing (as a new circuit) issuing of an EIC (electrical installation certificate) and notification via a registered body (NICEIC/NAPIT etc). It's also worth pointing out that if the work were not notified to your local building control (via a third party scheme or direct) you may encounter difficulties with your local building control/insurance/ potential buyers in the future, which will undoubtedly end up in further costs. This is really all there to ensure a/your safety and b/your enjoyment from your new garden room. Good Luck and enjoy 😁

Hi there, 6mm is not enough for the circuits you’re requiring. I’d go with SWA 20mm for the 35m you require. Hope this helps.